This invention relates to the testing of rails of railroad tracks, and more particularly to a method and apparatus for the non-destructive testing of the rails of railroad tracks in situ and continuously. device for the implementation of such a process.
The dynamic overloads and stresses to which the track is subjected cause the development of internal faults in the rail, such as oval flaws, horizontal, transverse or longitudinal cracks, star-shaped cracks, etc.
It is important to be able to detect these faults on the track using a non-destructive method, in order to be able to change defective sections of rail in time.
The most widely used method of non-destructive testing of the internal state of rail on the track is the sounding of the rail by ultrasonics. This technique consists in placing in contact with the rail head transmitting, receiving or transmitting-receiving probes, the orientation of which is adapted to the types of fault being looked for.
The picked up echoes of the transmitted ultrasonics are usually displayed on cathode ray screens. These echoes are also recorded graphically, which enables the position and type of the faults detected to be determined. The interpretation of the faults is also carried out with the help of a digital computer the printer of which delivers a direct report on the location and type of the faults.
The probes can be installed on trucks, rolling on the rails, and kept in sound contact with the metal of the rail by means of a film of water. It is also possible to use probes placed in a wheel rolling on the rail, the sound contact between the probe and the running surface being provided for example by a liquid enclosed in the wheel, as described in the U.S. Pat. No. 4,165,648.
The probes to be used and their positioning are determined by the characteristics of the faults to be detected. In use, it is important for each probe to remain constantly and accurately positioned with respect to the rail of the sounded track.
For probes working with a beam reflected at non-zero incidence under the rail bottom, the longitudinal spacing must be a function of the height of the rail for good reception. For probes to be used for looking for faults in the relatively narrow rail web, it is their transverse positioning with respect to the axis of the rail that must be accurately provided.
In certain existing embodiments, the lateral positioning of the probes with respect to the rail is produced by the forced pressure, by a jack or a spring, of a mechanical part rigidly connected to the probe carrying truck, against the internal lateral surface of the rail head considered as a transverse geometrical reference of the profile of the rail.
These embodiments have large disadvantages associated with the diversity in the widths of the rail heads of rails laid on the track, arising as much from the different types of rail laid as from the various degrees of lateral wear or excess width due to the crushing of the rail heads. The probes are therefore poorly positioned and cannot guarantee good testing quality.
On certain embodiments there are manual controls for the transverse and/or longitudinal positioning of the probes. These equipments are not however satisfactory, since these controls must be operated according to a visual observation of the state of the rail head, which can only lead to an approximate result and is deceptive above a certain speed of movement of the testing vehicle.
U.S. Pat. No. 4,044,594 describes a device for sounding a rail by means of a single probe housed in a wheel, necessitating a complex adjustment system to correct the lateral variations and the angular variations of the wheel resulting from irregularities in the surface of the rail. Such a device cannot operate efficiently at relatively high speeds.